A three-year prospective study of back pain will be carried out among 4,000 employees of the Allen-Bradley Company of Milwaukee, Wisconsin. Managerial, secretarial, clerical and industrial workers are to be included. The major descriptive outcomes of this study will be total and annual period prevalence rates, annual incidence rates, and recurrence rates of low back pain. Other outcome measures will include the frequency and duration of work loss due to low back pain, types of remedies attempted to relieve low back pain, perception of effectiveness of attempted remedies, and types of health professionals consulted for low back pain. In addition, a number of variables will be evaluated as potential risk factors for low back pain. These variables will describe personal characteristics, work environment and activities, and medical and family history. Additional variables are to include anthropometric measurements of height, weight, waist girth, elbow breadth (frame size) and two composite measures of obesity: Quetelet's index and relative weight. These measurements are to be obtained at the work site by nurse-coordinators. Baseline information on each employee will be obtained during the first year of the study from a self report questionnaire administered by nurse-coordinators at the work site. Follow-up information on the subsequent occurrence of low back pain will be retrieved from annual questionnaires, administered in the second and third years of the study, and from employees who report back pain symptomatology to the company Medical Department. Other sources of data will be job descriptions obtained by the nurse-coordinators. On the basis of previous published studies, it is anticipated that a number of the variables measured in this study will be significantly associated with the occurrence of low back pain in the study population. Other variables which will be measured have not been previously evaluated in a population-based study. The prospective design to be employed in this study will provide direct measurements of the risks of low back pain associated with each of these possible risk factors. In addition the large size of the study population will allow for more detailed analyses of these factors and the possible interactions between them than has been accomplished in previous studies.